This disclosure relates generally to light-emitting devices and in particular to an LED emitter that produces light having a continuous spectrum.
Light sources based on light-emitting diodes (LEDs) are emerging as an energy-efficient replacement for conventional incandescent or halogen light sources in a variety of applications. Compared to conventional light sources, LED-based light sources can provide significantly higher energy efficiency and longer life.
However, a number of challenges must be addressed to provide practical LED-based light sources. For example, a given LED emits light in a narrow band of wavelengths, which creates challenges for the production of white light (which is generally a mixture of different wavelengths). Further, not all white light is created equal. The human eye is sensitive to the differences among white-light sources such as fluorescent light, incandescent light, and sunlight. “Color temperature” generally refers to the spectrum of light produced by a black body radiator at a given temperature, and artificial light sources can be assigned a correlated color temperature (CCT) based on approximate color-matching to a blackbody radiator. Moreover, not all white light of a given CCT is equivalent. For instance, in the case of environmental lighting, the quality of light depends on its spectral content, which determines how objects of various colors will appear when illuminated by the light. Quality of color may be measured using various metrics, such as the widely used color rendering index (CRI, or “CIE Ra”), as defined by the International Commission on Illumination (CIE). CIE Ra is a quantitative measure of how accurately an artificial light source reproduces object color across a range of colors, as compared with natural light. The artificial light source can be tested using a number of CIE standard color samples; examples used herein are based on the standard R1-R15 sample set. Another measure of quality of color includes the “TM-30-15” color metrics recently published by the Illuminating Engineering Society (IES) (Technical Memorandum TM-30-15, entitled “IES Method for Evaluating Light Source Color Rendition”). TM-30-15 color metrics include a fidelity metric (Rf) similar to CRI and a gamut metric (Rg) that indicates average saturation level relative to a reference source. High CRI, or Rf and Rg close to 100, are desirable characteristics for a quality white light source.